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  1. #1
    Hi all,

    My first post after spending much time soaking up some really great ideas.

    I must confess though, I'm suffering from information-overload! - there's just too much to take in, and not be able to apply directly.

    Anyways, I've always wanted a cnc router - and now I finally get to build one . So, in preparation I've been trawling forums like yours and without doubt - you guys rock for friendly, solid advice.

    The beast:
    - I want something that I won't have to say, "damn...if only I had this (longer, wider, 4th axis, etc) or that!" I figure around 1200 x 800 x 300 (X,Y,Z as you guys reference it) would do nicely.
    - 4th axis is a requirement.
    - Working mainly wood and perspex but must be able to do aluminium as well. I don't mind shallower cuts, slower feed rate and/or more runs to do it, but I must be able to do it.
    - As accurate as possible, repeat-ability very important.
    - One thing I learned over the years from my electronics career is that when you do something, do it well (as you can, budget permitting) - and don't skimp! If you're investing in something, get the best you can afford, and if you can't afford it, save up for it.
    - I've only been considering Hiwin and/or SKF for the profile linear guides and rails and ballscrews.
    - Base:
    I'm thinking of going 50x50x3 square tubing for most of the frame. I've probably gone over-kill on the supports but what the hell - can't do any harm.
    Comments will be most welcome (thanks in advance :))

    - Axis:
    X (1200-ish):
    I was going to use a single ballscrew down the center, until I came across a post(s), I think from jazzcnc, that completely changed my approach (and kicked off yet another design iteration). I think it's a brilliant idea for the 4th axis and so this design based on it.
    I'm unsure whether to go with 2 x 12mm or 2 x 16mm x 5 (or 10) for the long axis. SKF (BK/BF) fixed and floating bearings.
    Profile rail guides and blocks SKF 15mm profile (LLTHR15 rail, LLTHC1 carriage).
    NEMA-23 3Nm stepper motors on either side, reverse polarity on one of them, driven from same driver board.

    Y (850-ish):
    For this axis I'm thinking of using Ally profile. There's a guy down here in my neck of the woods that has designed and has manufactured a really nice (versatile) 90x45 profile. A big advantage is that the rails (15 and 20) drop right into slots provided, and bolt down via t-bar.
    I'm also thinking of a "C-section" to beef it up some (see pics). MUCH more expensive than steel, but then a LOT less tinkering and engineering work negated - which probably justifies the decision. Also, I don't have access to the machinery you'd need to be able to work the engineering.
    Profile rail guides and blocks SKF 15mm profile (LLTHR15 rail, LLTHC1 carriage).
    12mm x 5 ballscrews, BK/BF end bearings again.
    NEMA-23 3Nm stepper motor.

    Z (300-ish):
    The main decision driver for the 300mm Z-axis is to be able to do up to about 150mm radius wood/perspex lathe work.
    Profile rail guides and blocks SKF 15mm profile (LLTHR15 rail, LLTHC1 carriage).
    12mm x 5 ballscrews, 15mm profile rail.
    NEMA-23 3Nm stepper motor, belt & pulley driven. No idea of ratios!

    4th Axis:
    100/110mm chuck and tailstock.
    90x45 Al profile across the front, provides for a moveable tailstock, running on the profile.
    NEMA-23 3Nm stepper, belt & pulley driven. No idea of ratios!

    Spindle:
    GDZ-80-1 Spindle motor, 12000-24000(RPM), 1.5(KW), 220(V), 5(A), 100-400(HZ) Φ80*188, water-cooled, ER11 Collet


    I'd love to buy the following spindle (http://www.cncdirect.co.za/htm/control.html) but it'll have to wait until I can justify the cost! And, there's no local stock at the moment!
    I'm a bit concerned with the Chinese spindle having read about guys having had to open them up to properly earth units, sub-standard wiring, and the likes! Hopefully this is not the case on this one.

    I'm as yet undecided on the breakout board to use.
    I'm very comfortable on Linux and was thinking of going with linuxcnc over mach. I can develop and/or write my own stuff, and/or add embedded controllers if and where necessary. Plus of course, it's free, and I have all resources on the PC available to me if needs be.



    Here are some links to the electronics I have in mind to use:
    Stepper motors: https://www.robotics.org.za/index.ph...product_id=123
    Drivers: https://www.robotics.org.za/index.ph...&product_id=69

    And, here are some pics for reference. I would really appreciate all the help and advice I can get.

    Click image for larger version. 

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    Thanks folks, appreciate.

    Cheers

  2. #2
    Ah, good to see another South African on the forum. I'm very much in the same boat as you trying to figure out what's the right direction for my build. There's much more knowledgeable people on here than me so I'll leave the comments on your design to them.


    Apart from the great build threads here's some of the stuff I found extremely helpfull with a design


    To calculate critical speed on ballskrews and motor sizing a great help is also. Can't find the link now but If search on here you'll find it
    MotorCalcs.zip


    Extremely usefull to compare stiffness of different design options.
    cnc_stiffness_calculator_v8 (look at post #26)
    http://www.mycncuk.com/threads/7733-...r-design/page3
    Or you can just spend endless time fidling with FEA software and be none the wiser :-)


    A few general comments:
    Helped a friend of mine build a router and he got those Wantai steppers and motors from MicroRobotics and he's very happy with them.


    Not sure what your requirements are wrt the 4th axis but be realistic in your expectations. I have a UniCam router with a 4th axis and I have not used that functionality in the 5 years I have the machine. Maybe it has changed recently but in my experience I have not found any reasonably priced software that can do true 4th axis toolpathing. Sure, if you want to engrave text around a cylinder there's plenty free stuff around that will wrap a 2d path around a cylinder.


    The stuff from CNCDirect are top notch. Piles of wood dust made on my router over the years and the SKF bearings are still smooth as silk. You may also consider the Hiwin rails. I ordered Hiwin rails from Wendy's Bearing Store http://www.aliexpress.com/store/637430 Payed on the Wednesday and they were in my hands the next friday so I'm very happy with her service and the rails seems to be of very good quality and probably comparable to the SKF suff. The chinese ballskrews and nuts is not comparable to the SKF producs but considering the price I think they are great value for money. I decided to give them a go so we'll see how that works out.


    Good luck with your build and if you find other useful local suppliers for the bits and pieces please let me know, I'll do the same.

  3. #3
    @lebies
    There are other things but for a start these jump out at me.

    1. A spindle with at least an ER20 collet is a MUST I would say, also a 2.2kW spindle would suit the machine better.
    2. The Z bearing blocks are too close together in the vertical direction, these will be weak regarding twisting as they are.
    3. With an X of 1200 you might find 16mm ball screws will whip at higher speed but I'll let jazzcnc comment on that, he might suggest changing the pitch to slow them down.
    4. You might need to think about 20mm rail instead of 15mm
    5. Rather than a long Z travel, think about an adjustable bed. The Z will be very weak at full extension as shown.

    I look forward to seeing your control panel design.
    Last edited by EddyCurrent; 12-08-2014 at 09:24 PM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  4. #4
    Hi Lebies,

    Welcome to the forum. Agree with Eddy, plus a couple more views on your design:

    That is a large machine to also cut aluminium. It's not so much about taking lighter cuts and going slowly to compensate for lower machine stiffness (which will be likely with a large machine), but just that you don't have the stiffness at the cutter so it will vibrate, get hot, and go blunt. To compensate you will end up beefing things up but at this size it all gets heavy and the design could run away with you. Just be realistic about what it could do at this size and don't expect too much on the aluminium cutting.

    You have a very large offset from the Z axis to the Y rails - I can see that you are trying to mount them on the rear part of the gantry where the gantry is locally stiffer, but I think you will be worse off overall due to the offset. I would mount them on the front of the gantry closer to the Y rails, then if the ballscrew clearance allows push the central extrusion forward as much as possible. Then close off the open back with a simple plate of moderate thickness, say 10mm. That way you are getting back towards an overall box section.

    The end plates on the gantry look very thin. I would use 12mm minimum here (aluminium), and for the ones underneath to mount to the X axis bearings.

    Will you add a bed to this? The spacing of the cross members of around 600mm is quite large. Another 2 member would be my minimum. Don't underestimate the bed stiffness as this is what hold the workpiece against the cutter forces. Vibration here is just as bad as vibration on the tool - difference is it is much easier to do something about by adding more support.

    X axis motors - you mention running them in opposite directions to each other? Not sure why you need to do that. They should normally run the same direction (both clockwise or both anti-clockwise) otherwise the gantry will be pulled into a serious racking problem! Perhaps you are confused about running twin ballscrews on one axis, or maybe I misunderstood your intentions there.

    Looking forward to see how it progresses. I'm sure you'll get plenty of other support as you go . . .
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  5. #5
    I'm very comfortable on Linux and was thinking of going with linuxcnc over mach. I can develop and/or write my own stuff
    If you are going to slave your x axis you might have to re think Linuxcnc unless you drive both screws from one motor. Linuxcnc don't seem to have a system for homing 2 motors (joints) there is a lot of debate over on the Linux forum about this. Its a shame its not been sorted by now. I use linuxcnc for my mill and Mach3 for the router. Driving both screws from one motor is no problem though. Good luck with the build. ..Clive

  6. #6
    Hey all,

    Thanks for the great input so far, I'm sure there'll be more as we go ... :).

    mitchejc
    Ah, good to see another South African on the forum...
    Thanks man,
    been lurking for a while now, and now I'm sorry I didn't get my act together and post a lot earlier.
    Thanks for the links, already learned from them...

    I'm really glad to hear the steppers are good enough, was a bit concerned there. I've used their smaller steppers on a project and also found them to be very good.
    Yep, Greg's stuff is very good, and he's a very knowledgeable and approachable guy as well. I'll definitely look into Wendy's. I sourced the local (jo'burg) Hiwin agent and got what I thought to be very reasonable prices from him. My main concern with China was the shipping time, but your deal is great as far as that's concerned. Also, I've heard that a lot of the Hiwin stuff coming from China is not the same quality that comes from the Taiwan factory. Apparently they pick up the stuff (from Hiwin) that doesn't quite make Hiwin's standard, and sell that. i.e. it's not reject, just not what you'd get from the original manufacturer. I'd be interested in hearing how yours go for you.

    As for the 4th Axis, you guys are all right, I'm probably overstepping the bounds. I'm going to reduce the 4th axis radius to around 75mm (1/2 it). Then again I hear what you're saying, and will look into the whole software thing in a lot more depth ... even if I have to look at writing something to accommodate (on the longer term).

    EddyCurrent
    There are other things but for a start these jump out at me...
    Thanks for this.
    1. I'll take your good advice and source the suggested spindle and collet.
    2. I am going to reduce the working radius on my 4th axis (hence the longer travel) and go to around half of it. I'll also increase the distance between the blocks as suggested. What should I look at for a minimum please?
    3. Hopefully jazzcnc does comment, I'd be very interested in hearing his suggestions.
    4. I started out on 20mm rail originally, only to be told by the manufacturers that 15 would more than suffice in terms of loading, etc. As I downsize the Z axis, I'm going to also downsize on the other axis as well. Not a whole lot, but a fair amount.
    5. With the reduced Z axis and added other suggestions, I don't think I want to go adjustable table (for now anyways).

    routercnc
    That is a large machine to also cut aluminium...
    Agreed. The main materials I'll be working with will be hardwood and perspex. For the occasions I'll want to work ally, it probably doesn't justify it anyway.

    You have a very large offset from the Z axis to the Y rails - ...
    There's another way I can do the Y-axis, and that's to use 2 of those profiles atop of each other, i.e loose the center piece - but that's if I insist on going that route. If I do, although simpler, it's a hellova lot more expensive and again, probably not worth the expense. I'll look at going back to an earlier design which was an all steel machine (and stop being so damned lazy :) ). In that version, I got the the ratio down much better.

    The end plates on the gantry look very thin.

    My bad! I should have said the end plates are 5mm steel plate, as are the gantry cross plate (bottom plate) and 4th axis mount plate.

    Will you add a bed to this?

    Yep, 32mm MDF, and I'll add 2 additional cross members to stiffen it up as well as suggested.

    X axis motors
    Yes, I got THAT one wrong, didn't I :). Not quite sure what I was thinking of on this one, probably one of my earlier version designs!

    Clive S
    If you are going to slave your x axis you might have to re think Linuxcnc ...

    Thanks for pointing this one out to me. I'll rehash it and also better research it.

    Thanks all so far for the great feedback. With you all pointing me in the right directions I'm really looking forward to getting this thing done.


  7. #7
    Quote Originally Posted by lebies View Post
    I'll also increase the distance between the blocks as suggested. [I]What should I look at for a minimum please?
    Well mine have a gap of 95mm, that is inner face to inner face, I calculated that as the best for my machine.

    With regard to the bed, I urge you to use birch plywood rather than MDF. I used two layers of 19mm and sealed it all with a 50/50 mix of polyurethane varnish and danish oil. That's after leveling the bed by running some G code to run the router over it with a large end mill cutter.

    With regard to aluminium, I thought I might do some cutting of this myself but when you consider the requirements for lubrication/coolant, a wood cutting router just does not have the appropriate bed arrangement.
    You might want to think about that in your design before starting the build i.e. an aluminium T slot bed might be a better alternative.
    Last edited by EddyCurrent; 13-08-2014 at 10:16 PM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  8. #8
    Quote Originally Posted by EddyCurrent View Post

    With regard to aluminium, I thought I might do some cutting of this myself but when you consider the requirements for lubrication/coolant, a wood cutting router just does not have the appropriate bed arrangement.
    You might want to think about that in your design before starting the build i.e. an aluminium T slot bed might be a better alternative.
    One of the best ways to cut aluminum is to use old fridge compressor that blows cheap airbrush that spays mist of alcohol at the cutter. The mist evaporates instantly and leaves everything dry and cool. So coolant is not a problem.

  9. #9
    Quote Originally Posted by silyavski View Post
    One of the best ways to cut aluminum is to use old fridge compressor that blows cheap airbrush that spays mist of alcohol at the cutter. The mist evaporates instantly and leaves everything dry and cool. So coolant is not a problem.
    Cool (no pun intended) idea :) ...

    After all your initial input (for which I'm very grateful thanks), here's take 2:

    - Z-Axis travel now 100mm (all dims +-)
    - Y & Z axis now welded plate (mainly 5mm with 8mm spindle mount plate.
    - Used 100x50x4 to mount X and Y-axis rails onto
    - Widened guide rail blocks all-round

    A pic paints a 1000 words ... so here ya go (2ns is just the Y-bed detail construction):

    Click image for larger version. 

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    As always, your feedback valued :)...

  10. #10
    Quote Originally Posted by EddyCurrent View Post
    Well mine have a gap of 95mm, that is inner face to inner face, I calculated that as the best for my machine.

    With regard to the bed, I urge you to use birch plywood rather than MDF. I used two layers of 19mm and sealed it all with a 50/50 mix of polyurethane varnish and danish oil. That's after leveling the bed by running some G code to run the router over it with a large end mill cutter.
    Done ... thanks.


    Quote Originally Posted by EddyCurrent View Post
    With regard to aluminium, I thought I might do some cutting of this myself but when you consider the requirements for lubrication/coolant, a wood cutting router just does not have the appropriate bed arrangement.
    You might want to think about that in your design before starting the build i.e. an aluminium T slot bed might be a better alternative.
    Have rehashed my thinking. I'll be able to do it on my updated version but it's no longer a high priority.

    I wanted to use the al T-slot bed, but I'll buy it piece-meal for future. This stuff is extremely expensive around here - very, very nice, but damned costly for now :).

    Thanks for your help, appreciate.

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